On Fri, 29 Jul 2022, Qing Zhao wrote:
> Hi, Richard,
>
> Thanks a lot for your comments and suggestions. (And sorry for my late reply).
>
> > On Jul 28, 2022, at 3:26 AM, Richard Biener <rguent...@suse.de> wrote:
> >
> > On Tue, 19 Jul 2022, Qing Zhao wrote:
> >
> >> From 3854004802b8e2f132ebf218fc35a632f5e80c6a Mon Sep 17 00:00:00 2001
> >> From: Qing Zhao <qing.z...@oracle.com>
> >> Date: Mon, 18 Jul 2022 17:04:12 +0000
> >> Subject: [PATCH 1/2] Add a new option -fstrict-flex-array[=n] and new
> >> attribute strict_flex_array
> >>
> >> Add the following new option -fstrict-flex-array[=n] and a corresponding
> >> attribute strict_flex_array to GCC:
> >>
> >> '-fstrict-flex-array'
> >> Treat the trailing array of a structure as a flexible array member
> >> in a stricter way. The positive form is equivalent to
> >> '-fstrict-flex-array=3', which is the strictest. A trailing array
> >> is treated as a flexible array member only when it is declared as a
> >> flexible array member per C99 standard onwards. The negative form
> >> is equivalent to '-fstrict-flex-array=0', which is the least
> >> strict. All trailing arrays of structures are treated as flexible
> >> array members.
> >>
> >> '-fstrict-flex-array=LEVEL'
> >> Treat the trailing array of a structure as a flexible array member
> >> in a stricter way. The value of LEVEL controls the level of
> >> strictness.
> >>
> >> The possible values of LEVEL are the same as for the
> >> 'strict_flex_array' attribute (*note Variable Attributes::).
> >>
> >> You can control this behavior for a specific trailing array field
> >> of a structure by using the variable attribute 'strict_flex_array'
> >> attribute (*note Variable Attributes::).
> >>
> >> 'strict_flex_array (LEVEL)'
> >> The 'strict_flex_array' attribute should be attached to the
> >> trailing array field of a structure. It specifies the level of
> >> strictness of treating the trailing array field of a structure as a
> >> flexible array member. LEVEL must be an integer betwen 0 to 3.
> >>
> >> LEVEL=0 is the least strict level, all trailing arrays of
> >> structures are treated as flexible array members. LEVEL=3 is the
> >> strictest level, only when the trailing array is declared as a
> >> flexible array member per C99 standard onwards ([]), it is treated
> >> as a flexible array member.
> >>
> >> There are two more levels in between 0 and 3, which are provided to
> >> support older codes that use GCC zero-length array extension ([0])
> >> or one-size array as flexible array member ([1]): When LEVEL is 1,
> >> the trailing array is treated as a flexible array member when it is
> >> declared as either [], [0], or [1]; When LEVEL is 2, the trailing
> >> array is treated as a flexible array member when it is declared as
> >> either [], or [0].
> >>
> >> This attribute can be used with or without '-fstrict-flex-array'.
> >> When both the attribute and the option present at the same time,
> >> the level of the strictness for the specific trailing array field
> >> is determined by the attribute.
> >>
> >> gcc/c-family/ChangeLog:
> >>
> >> * c-attribs.cc (handle_strict_flex_array_attribute): New function.
> >> (c_common_attribute_table): New item for strict_flex_array.
> >> * c.opt (fstrict-flex-array): New option.
> >> (fstrict-flex-array=): New option.
> >>
> >> gcc/c/ChangeLog:
> >>
> >> * c-decl.cc (add_flexible_array_elts_to_size): Call new utility
> >> routine flexible_array_member_p.
> >> (is_flexible_array_member_p): New function.
> >> (finish_struct): Set the new DECL_NOT_FLEXARRAY flag.
> >>
> >> gcc/ChangeLog:
> >>
> >> * doc/extend.texi: Document strict_flex_array attribute.
> >> * doc/invoke.texi: Document -fstrict-flex-array[=n] option.
> >> * tree-core.h (struct tree_decl_common): New bit field
> >> decl_not_flexarray.
> >> * tree.cc (component_ref_size): Reorg by using new utility functions.
> >> (flexible_array_member_p): New function.
> >> (zero_length_array_p): Likewise.
> >> (one_element_array_p): Likewise.
> >> (flexible_array_type_p): Likewise.
> >> * tree.h (DECL_NOT_FLEXARRAY): New flag.
> >> (zero_length_array_p): New function prototype.
> >> (one_element_array_p): Likewise.
> >> (flexible_array_member_p): Likewise.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> * gcc.dg/strict-flex-array-1.c: New test.
> >> ---
> >> gcc/c-family/c-attribs.cc | 47 ++++++++
> >> gcc/c-family/c.opt | 7 ++
> >> gcc/c/c-decl.cc | 91 +++++++++++++--
> >> gcc/doc/extend.texi | 25 ++++
> >> gcc/doc/invoke.texi | 27 ++++-
> >> gcc/testsuite/gcc.dg/strict-flex-array-1.c | 31 +++++
> >> gcc/tree-core.h | 5 +-
> >> gcc/tree.cc | 130 ++++++++++++++-------
> >> gcc/tree.h | 16 ++-
> >> 9 files changed, 322 insertions(+), 57 deletions(-)
> >> create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-1.c
> >>
> >> diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
> >> index c8d96723f4c..10d16532f0d 100644
> >> --- a/gcc/c-family/c-attribs.cc
> >> +++ b/gcc/c-family/c-attribs.cc
> >> @@ -101,6 +101,8 @@ static tree handle_special_var_sec_attribute (tree *,
> >> tree, tree, int, bool *);
> >> static tree handle_aligned_attribute (tree *, tree, tree, int, bool *);
> >> static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree,
> >> int, bool *);
> >> +static tree handle_strict_flex_array_attribute (tree *, tree, tree,
> >> + int, bool *);
> >> static tree handle_weak_attribute (tree *, tree, tree, int, bool *) ;
> >> static tree handle_noplt_attribute (tree *, tree, tree, int, bool *) ;
> >> static tree handle_alias_ifunc_attribute (bool, tree *, tree, tree, bool
> >> *);
> >> @@ -367,6 +369,8 @@ const struct attribute_spec c_common_attribute_table[]
> >> =
> >> attr_aligned_exclusions },
> >> { "warn_if_not_aligned", 0, 1, false, false, false, false,
> >> handle_warn_if_not_aligned_attribute, NULL },
> >> + { "strict_flex_array", 1, 1, false, false, false, false,
> >> + handle_strict_flex_array_attribute, NULL },
> >> { "weak", 0, 0, true, false, false, false,
> >> handle_weak_attribute, NULL },
> >> { "noplt", 0, 0, true, false, false, false,
> >> @@ -2498,6 +2502,49 @@ handle_warn_if_not_aligned_attribute (tree *node,
> >> tree name,
> >> no_add_attrs, true);
> >> }
> >>
> >> +/* Handle a "strict_flex_array" attribute; arguments as in
> >> + struct attribute_spec.handler. */
> >> +
> >> +static tree
> >> +handle_strict_flex_array_attribute (tree *node, tree name,
> >> + tree args, int ARG_UNUSED (flags),
> >> + bool *no_add_attrs)
> >> +{
> >> + tree decl = *node;
> >> + tree argval = TREE_VALUE (args);
> >> +
> >> + /* This attribute only applies to field decls of a structure. */
> >> + if (TREE_CODE (decl) != FIELD_DECL)
> >> + {
> >> + error_at (DECL_SOURCE_LOCATION (decl),
> >> + "%qE attribute may not be specified for %q+D", name, decl);
> >> + *no_add_attrs = true;
> >> + }
> >> + /* This attribute only applies to field with array type. */
> >> + else if (TREE_CODE (TREE_TYPE (decl)) != ARRAY_TYPE)
> >> + {
> >> + error_at (DECL_SOURCE_LOCATION (decl),
> >> + "%qE attribute may not be specified for a non array field",
> >> + name);
> >> + *no_add_attrs = true;
> >> + }
> >> + else if (TREE_CODE (argval) != INTEGER_CST)
> >> + {
> >> + error_at (DECL_SOURCE_LOCATION (decl),
> >> + "%qE attribute argument not an integer", name);
> >> + *no_add_attrs = true;
> >> + }
> >> + else if (!tree_fits_uhwi_p (argval) || tree_to_uhwi (argval) > 3)
> >> + {
> >> + error_at (DECL_SOURCE_LOCATION (decl),
> >> + "%qE attribute argument %qE is not an integer constant"
> >> + " between 0 and 3", name, argval);
> >> + *no_add_attrs = true;
> >> + }
> >> +
> >> + return NULL_TREE;
> >> +}
> >> +
> >> /* Handle a "weak" attribute; arguments as in
> >> struct attribute_spec.handler. */
> >>
> >> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> >> index 44e1a60ce24..864cd8df1d3 100644
> >> --- a/gcc/c-family/c.opt
> >> +++ b/gcc/c-family/c.opt
> >> @@ -2060,6 +2060,13 @@ fsized-deallocation
> >> C++ ObjC++ Var(flag_sized_deallocation) Init(-1)
> >> Enable C++14 sized deallocation support.
> >>
> >> +fstrict-flex-array
> >> +C C++ Common Alias(fstrict-flex-array=,3,0)
> >> +
> >> +fstrict-flex-array=
> >> +C C++ Common Joined RejectNegative UInteger Var(flag_strict_flex_array)
> >> Init(0) IntegerRange(0,3)
> >> +-fstrict-flex-array=<level> Treat the trailing array of a structure as
> >> a flexible array in a stricter way. The default is treating all trailing
> >> arrays of structures as flexible arrays.
> >> +
> >> fsquangle
> >> C++ ObjC++ WarnRemoved
> >>
> >> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> >> index ae8990c138f..14defae9584 100644
> >> --- a/gcc/c/c-decl.cc
> >> +++ b/gcc/c/c-decl.cc
> >> @@ -5013,10 +5013,7 @@ add_flexible_array_elts_to_size (tree decl, tree
> >> init)
> >>
> >> elt = CONSTRUCTOR_ELTS (init)->last ().value;
> >> type = TREE_TYPE (elt);
> >> - if (TREE_CODE (type) == ARRAY_TYPE
> >> - && TYPE_SIZE (type) == NULL_TREE
> >> - && TYPE_DOMAIN (type) != NULL_TREE
> >> - && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> >> + if (flexible_array_member_p (type))
> >> {
> >> complete_array_type (&type, elt, false);
> >> DECL_SIZE (decl)
> >> @@ -8720,6 +8717,80 @@ finish_incomplete_vars (tree incomplete_vars, bool
> >> toplevel)
> >> }
> >> }
> >>
> >> +/* Determine whether the FIELD_DECL X is a flexible array member
> >> according to
> >> + the following info:
> >> + A. whether the FIELD_DECL X is the last field of the DECL_CONTEXT;
> >> + B. whether the FIELD_DECL is an array that is declared as "[]", "[0]",
> >> + or "[1]";
> >> + C. flag_strict_flex_array;
> >> + D. the attribute strict_flex_array that is attached to the field
> >> + if presenting.
> >> + Return TRUE when it's a flexible array member, FALSE otherwise. */
> >> +
> >> +static bool
> >> +is_flexible_array_member_p (bool is_last_field,
> >> + tree x)
> >> +{
> >> + /* if not the last field, return false. */
> >> + if (!is_last_field)
> >> + return false;
> >> +
> >> + /* if not an array field, return false. */
> >> + if (TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE)
> >> + return false;
> >> +
> >> + bool is_zero_length_array = zero_length_array_p (TREE_TYPE (x));
> >> + bool is_one_element_array = one_element_array_p (TREE_TYPE (x));
> >> + bool is_flexible_array = flexible_array_member_p (TREE_TYPE (x));
> >> +
> >> + unsigned int strict_flex_array_level = flag_strict_flex_array;
> >> +
> >> + tree attr_strict_flex_array = lookup_attribute ("strict_flex_array",
> >> + DECL_ATTRIBUTES (x));
> >> + /* if there is a strict_flex_array attribute attached to the field,
> >> + override the flag_strict_flex_array. */
> >> + if (attr_strict_flex_array)
> >> + {
> >> + /* get the value of the level first from the attribute. */
> >> + unsigned HOST_WIDE_INT attr_strict_flex_array_level = 0;
> >> + gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE);
> >> + attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array);
> >> + gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE);
> >> + attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array);
> >> + gcc_assert (tree_fits_uhwi_p (attr_strict_flex_array));
> >> + attr_strict_flex_array_level = tree_to_uhwi
> >> (attr_strict_flex_array);
> >> +
> >> + /* the attribute has higher priority than flag_struct_flex_array.
> >> */
> >> + strict_flex_array_level = attr_strict_flex_array_level;
> >> + }
> >> +
> >> + switch (strict_flex_array_level)
> >> + {
> >> + case 0:
> >> + /* default, all trailing arrays are flexiable array members. */
> >> + return true;
> >> + case 1:
> >> + /* Level 1: all "[1]", "[0]", and "[]" are flexiable array members. */
> >> + if (is_one_element_array)
> >> + return true;
> >> + /* FALLTHROUGH. */
> >> + case 2:
> >> + /* Level 2: all "[0]", and "[]" are flexiable array members. */
> >> + if (is_zero_length_array)
> >> + return true;
> >> + /* FALLTHROUGH. */
> >> + case 3:
> >> + /* Level 3: Only "[]" are flexible array members. */
> >> + if (is_flexible_array)
> >> + return true;
> >> + break;
> >> + default:
> >> + gcc_unreachable ();
> >> + }
> >> + return false;
> >> +}
> >> +
> >> +
> >> /* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T.
> >> LOC is the location of the RECORD_TYPE or UNION_TYPE's definition.
> >> FIELDLIST is a chain of FIELD_DECL nodes for the fields.
> >> @@ -8781,6 +8852,8 @@ finish_struct (location_t loc, tree t, tree
> >> fieldlist, tree attributes,
> >> bool saw_named_field = false;
> >> for (x = fieldlist; x; x = DECL_CHAIN (x))
> >> {
> >> + bool is_last_field = (DECL_CHAIN (x) == NULL_TREE);
> >> +
> >> if (TREE_TYPE (x) == error_mark_node)
> >> continue;
> >>
> >> @@ -8819,10 +8892,7 @@ finish_struct (location_t loc, tree t, tree
> >> fieldlist, tree attributes,
> >> DECL_PACKED (x) = 1;
> >>
> >> /* Detect flexible array member in an invalid context. */
> >> - if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE
> >> - && TYPE_SIZE (TREE_TYPE (x)) == NULL_TREE
> >> - && TYPE_DOMAIN (TREE_TYPE (x)) != NULL_TREE
> >> - && TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (x))) == NULL_TREE)
> >> + if (flexible_array_member_p (TREE_TYPE (x)))
> >> {
> >> if (TREE_CODE (t) == UNION_TYPE)
> >> {
> >> @@ -8830,7 +8900,7 @@ finish_struct (location_t loc, tree t, tree
> >> fieldlist, tree attributes,
> >> "flexible array member in union");
> >> TREE_TYPE (x) = error_mark_node;
> >> }
> >> - else if (DECL_CHAIN (x) != NULL_TREE)
> >> + else if (!is_last_field)
> >> {
> >> error_at (DECL_SOURCE_LOCATION (x),
> >> "flexible array member not at end of struct");
> >> @@ -8850,6 +8920,9 @@ finish_struct (location_t loc, tree t, tree
> >> fieldlist, tree attributes,
> >> pedwarn (DECL_SOURCE_LOCATION (x), OPT_Wpedantic,
> >> "invalid use of structure with flexible array member");
> >>
> >> + /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x. */
> >> + DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p
> >> (is_last_field, x);
> >> +
> >> if (DECL_NAME (x)
> >> || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
> >> saw_named_field = true;
> >> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> >> index dfbe33ac652..7451410a011 100644
> >> --- a/gcc/doc/extend.texi
> >> +++ b/gcc/doc/extend.texi
> >> @@ -7436,6 +7436,31 @@ This warning can be disabled by
> >> @option{-Wno-if-not-aligned}.
> >> The @code{warn_if_not_aligned} attribute can also be used for types
> >> (@pxref{Common Type Attributes}.)
> >>
> >> +@cindex @code{strict_flex_array} variable attribute
> >> +@item strict_flex_array (@var{level})
> >> +The @code{strict_flex_array} attribute should be attached to the trailing
> >> +array field of a structure. It specifies the level of strictness of
> >> +treating the trailing array field of a structure as a flexible array
> >> +member. @var{level} must be an integer betwen 0 to 3.
> >> +
> >> +@var{level}=0 is the least strict level, all trailing arrays of structures
> >> +are treated as flexible array members. @var{level}=3 is the strictest
> >> level,
> >> +only when the trailing array is declared as a flexible array member per
> >> C99
> >> +standard onwards ([]), it is treated as a flexible array member.
> >
> > How is level 3 (thus -fstrict-flex-array) interpreted when you specify
> > -std=c89? How for -std=gnu89?
>
> 1. what’s the major difference between -std=c89 and -std=gnu89 on flexible
> array? (Checked online, cannot find a concrete answer on this).
> ** my understanding is: -std=c89 will not support any flexible array
> (neither [], [0], [1]), but -std=gnu89 will support [0] and [1], but not [].
> Is this correct?
Yes.
> If my answer to the first question is correct, then:
>
> 2. When -fstrict-flex-array=n and -std=c89 present at the same time, which
> one has the higher priority?
> ** I think that -std=c89 should be honored over -fstrict-flex-array,
> therefore we should disable -fstrict-flex-array=n when n > 0 and issue
> warnings to the user.
>
>
> 3. how about -fstrict-flex-array=n and -std=gnu89 present at the same time?
> ** When -std=gnu89 present, [] is not supported. So, we need to issue
> an warning to disable -fstrict-flex-array=3; but level 1 and level 2 is Okay.
>
> We also need to document the above.
>
> Let me know if you have any more comment and suggestions here.
In my opinion -fstrict-flex-array only makes sense with C99 and above.
The extra sub-levels allowing [0] or [1] are of questionable benefit.
I think that with -fstrict-flex-array we're missing a -Wstrict-flex-array
that would diagnose accesses that are no longer treated as flex array
access but would be without -fstrict-flex-array? The goal of
-fstrict-flex-array + -Wstrict-flex-array is to make code standard
conformant, no? Not to enable extra optimization for [1] arrays when
we know [0] is used as flexarray?
> >
> >> +
> >> +There are two more levels in between 0 and 3, which are provided to
> >> support
> >> +older codes that use GCC zero-length array extension ([0]) or one-size
> >> array
> >> +as flexible array member ([1]):
> >> +When @var{level} is 1, the trailing array is treated as a flexible array
> >> member
> >> +when it is declared as either "[]", "[0]", or "[1]";
> >> +When @var{level} is 2, the trailing array is treated as a flexible array
> >> member
> >> +when it is declared as either "[]", or "[0]".
> >
> > Given the above does adding level 2 make sense given that [0] is a GNU
> > extension?
> I think Kees already answered this question.
> >
> >> +This attribute can be used with or without @option{-fstrict-flex-array}.
> >> When
> >> +both the attribute and the option present at the same time, the level of
> >> the
> >> +strictness for the specific trailing array field is determined by the
> >> attribute.
> >> +
> >> +
> >> @item alloc_size (@var{position})
> >> @itemx alloc_size (@var{position-1}, @var{position-2})
> >> @cindex @code{alloc_size} variable attribute
> >> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> >> index 94fe57aa4e2..9befe601817 100644
> >> --- a/gcc/doc/invoke.texi
> >> +++ b/gcc/doc/invoke.texi
> >> @@ -207,7 +207,8 @@ in the following sections.
> >> -fopenmp -fopenmp-simd @gol
> >> -fpermitted-flt-eval-methods=@var{standard} @gol
> >> -fplan9-extensions -fsigned-bitfields -funsigned-bitfields @gol
> >> --fsigned-char -funsigned-char -fsso-struct=@var{endianness}}
> >> +-fsigned-char -funsigned-char -fstrict-flex-array[=@var{n}] @gol
> >> +-fsso-struct=@var{endianness}}
> >>
> >> @item C++ Language Options
> >> @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
> >> @@ -2825,6 +2826,30 @@ The type @code{char} is always a distinct type from
> >> each of
> >> @code{signed char} or @code{unsigned char}, even though its behavior
> >> is always just like one of those two.
> >>
> >> +@item -fstrict-flex-array
> >> +@opindex fstrict-flex-array
> >> +@opindex fno-strict-flex-array
> >> +Treat the trailing array of a structure as a flexible array member in a
> >> +stricter way.
> >> +The positive form is equivalent to @option{-fstrict-flex-array=3}, which
> >> is the
> >> +strictest. A trailing array is treated as a flexible array member only
> >> when it
> >> +is declared as a flexible array member per C99 standard onwards.
> >> +The negative form is equivalent to @option{-fstrict-flex-array=0}, which
> >> is the
> >> +least strict. All trailing arrays of structures are treated as flexible
> >> array
> >> +members.
> >> +
> >> +@item -fstrict-flex-array=@var{level}
> >> +@opindex fstrict-flex-array=@var{level}
> >> +Treat the trailing array of a structure as a flexible array member in a
> >> +stricter way. The value of @var{level} controls the level of strictness.
> >> +
> >> +The possible values of @var{level} are the same as for the
> >> +@code{strict_flex_array} attribute (@pxref{Variable Attributes}).
> >> +
> >> +You can control this behavior for a specific trailing array field of a
> >> +structure by using the variable attribute @code{strict_flex_array}
> >> attribute
> >> +(@pxref{Variable Attributes}).
> >> +
> >> @item -fsso-struct=@var{endianness}
> >> @opindex fsso-struct
> >> Set the default scalar storage order of structures and unions to the
> >> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-1.c
> >> b/gcc/testsuite/gcc.dg/strict-flex-array-1.c
> >> new file mode 100644
> >> index 00000000000..ec886c99b25
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-1.c
> >> @@ -0,0 +1,31 @@
> >> +/* testing the correct usage of attribute strict_flex_array. */
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2" } */
> >> +
> >> +
> >> +int x __attribute__ ((strict_flex_array (1))); /* { dg-error
> >> "'strict_flex_array' attribute may not be specified for 'x'" } */
> >> +
> >> +struct trailing {
> >> + int a;
> >> + int c __attribute ((strict_flex_array)); /* { dg-error "wrong number
> >> of arguments specified for 'strict_flex_array' attribute" } */
> >> +};
> >> +
> >> +struct trailing_1 {
> >> + int a;
> >> + int b;
> >> + int c __attribute ((strict_flex_array (2))); /* { dg-error
> >> "'strict_flex_array' attribute may not be specified for a non array field"
> >> } */
> >> +};
> >> +
> >> +extern int d;
> >> +
> >> +struct trailing_array_2 {
> >> + int a;
> >> + int b;
> >> + int c[1] __attribute ((strict_flex_array (d))); /* { dg-error
> >> "'strict_flex_array' attribute argument not an integer" } */
> >> +};
> >> +
> >> +struct trailing_array_3 {
> >> + int a;
> >> + int b;
> >> + int c[0] __attribute ((strict_flex_array (5))); /* { dg-error
> >> "'strict_flex_array' attribute argument '5' is not an integer constant
> >> between 0 and 3" } */
> >> +};
> >> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> >> index ea9f281f1cc..458c6e6ceea 100644
> >> --- a/gcc/tree-core.h
> >> +++ b/gcc/tree-core.h
> >> @@ -1813,7 +1813,10 @@ struct GTY(()) tree_decl_common {
> >> TYPE_WARN_IF_NOT_ALIGN. */
> >> unsigned int warn_if_not_align : 6;
> >>
> >> - /* 14 bits unused. */
> >> + /* In FIELD_DECL, this is DECL_NOT_FLEXARRAY. */
> >> + unsigned int decl_not_flexarray : 1;
> >> +
> >> + /* 13 bits unused. */
> >
> > I've not seen it so you are probably missing it - the bit has to be
> > streamed in tree-streamer-{in,out}.cc to be usable from LTO.
>
> You mean add it to the routine “unpack_ts_decl_common_value_fields” of
> tree-streamer-in.cc
> And “pack_ts_decl_common_value_fields” of tree-streamer-out.cc?
Yes.
>
> > C++ module streaming also needs to handle it.
>
> Which file is for this C++ module streaming?
Not sure, maybe cp/module.cc
> >
> >>
> >> /* UID for points-to sets, stable over copying from inlining. */
> >> unsigned int pt_uid;
> >> diff --git a/gcc/tree.cc b/gcc/tree.cc
> >> index 84000dd8b69..02e274699fb 100644
> >> --- a/gcc/tree.cc
> >> +++ b/gcc/tree.cc
> >> @@ -12862,7 +12862,7 @@ get_initializer_for (tree init, tree decl)
> >> /* Determines the size of the member referenced by the COMPONENT_REF
> >> REF, using its initializer expression if necessary in order to
> >> determine the size of an initialized flexible array member.
> >> - If non-null, set *ARK when REF refers to an interior zero-length
> >> + If non-null, set *SAM when REF refers to an interior zero-length
> >> array or a trailing one-element array.
> >> Returns the size as sizetype (which might be zero for an object
> >> with an uninitialized flexible array member) or null if the size
> >> @@ -12878,16 +12878,32 @@ component_ref_size (tree ref,
> >> special_array_member *sam /* = NULL */)
> >> sam = &sambuf;
> >> *sam = special_array_member::none;
> >>
> >> + /* Whether this ref is an array at the end of a structure. */
> >> + bool trailing = array_at_struct_end_p (ref);
> >> +
> >
> > actually array_at_struct_end_p returns whether ref possibly refers to
> > a trailing array. In particular it may return false for arrays at
> > struct end with a known length as in a.b[i] for the reference to global
> > 'a':
> >
> > struct { int b[1]; } a;
>
> Yes, I noticed this behavior during my recent debugging of this routine. I
> thought it’s a bug and planned to file another bug against it.
> Looks like that this is an expected behavior.
>
> Then I really feel the name and the comments of the routine is very confusing…
> Shall we change the name of this routine to a more descriptive one? For
> example, “flexible_array_member_p”?
Note the routine is about classifying a concrete reference, so a better
name could be flex_array_ref_p (). The name change should be done
separately (if at all).
> >
> > so in the end it should be array_at_struct_end_p also honoring
> > DECL_NOT_FLEXARRAY.
>
> Then it’s make more sense to check DECL_NOT_FLEXARRAY inside this utility
> routine?
Yes.
> >
> >> /* The object/argument referenced by the COMPONENT_REF and its type. */
> >> tree arg = TREE_OPERAND (ref, 0);
> >> tree argtype = TREE_TYPE (arg);
> >> - /* The referenced member. */
> >> - tree member = TREE_OPERAND (ref, 1);
> >>
> >> + /* The referenced field member. */
> >> + tree member = TREE_OPERAND (ref, 1);
> >> + tree memtype = TREE_TYPE (member);
> >> tree memsize = DECL_SIZE_UNIT (member);
> >> +
> >> + bool is_zero_length_array_ref = zero_length_array_p (memtype);
> >> + bool is_constant_length_array_ref = false;
> >> + bool is_one_element_array_ref
> >> + = one_element_array_p (memtype, &is_constant_length_array_ref);
> >> +
> >> + /* Determine the type of the special array member. */
> >> + if (is_zero_length_array_ref)
> >> + *sam = trailing ? special_array_member::trail_0
> >> + : special_array_member::int_0;
> >> + else if (is_one_element_array_ref && trailing)
> >> + *sam = special_array_member::trail_1;
> >> +
> >> if (memsize)
> >> {
> >> - tree memtype = TREE_TYPE (member);
> >> if (TREE_CODE (memtype) != ARRAY_TYPE)
> >> /* DECL_SIZE may be less than TYPE_SIZE in C++ when referring
> >> to the type of a class with a virtual base which doesn't
> >> @@ -12897,50 +12913,30 @@ component_ref_size (tree ref,
> >> special_array_member *sam /* = NULL */)
> >> return (tree_int_cst_equal (memsize, TYPE_SIZE_UNIT (memtype))
> >> ? memsize : NULL_TREE);
> >>
> >> - bool trailing = array_at_struct_end_p (ref);
> >> - bool zero_length = integer_zerop (memsize);
> >> - if (!trailing && !zero_length)
> >> + if (!trailing && !is_zero_length_array_ref)
> >> /* MEMBER is either an interior array or is an array with
> >> more than one element. */
> >> return memsize;
> >>
> >> - if (zero_length)
> >> - {
> >> - if (trailing)
> >> - *sam = special_array_member::trail_0;
> >> - else
> >> - {
> >> - *sam = special_array_member::int_0;
> >> - memsize = NULL_TREE;
> >> - }
> >> - }
> >> + if (*sam != special_array_member::trail_1
> >> + && is_constant_length_array_ref)
> >> + /* MEMBER is a constant length array which is not a one-element
> >> + trailing array. */
> >> + return memsize;
> >>
> >> - if (!zero_length)
> >> - if (tree dom = TYPE_DOMAIN (memtype))
> >> - if (tree min = TYPE_MIN_VALUE (dom))
> >> - if (tree max = TYPE_MAX_VALUE (dom))
> >> - if (TREE_CODE (min) == INTEGER_CST
> >> - && TREE_CODE (max) == INTEGER_CST)
> >> - {
> >> - offset_int minidx = wi::to_offset (min);
> >> - offset_int maxidx = wi::to_offset (max);
> >> - offset_int neltsm1 = maxidx - minidx;
> >> - if (neltsm1 > 0)
> >> - /* MEMBER is an array with more than one element. */
> >> - return memsize;
> >> -
> >> - if (neltsm1 == 0)
> >> - *sam = special_array_member::trail_1;
> >> - }
> >> + if (*sam == special_array_member::int_0)
> >> + memsize = NULL_TREE;
> >>
> >> - /* For a reference to a zero- or one-element array member of a union
> >> - use the size of the union instead of the size of the member. */
> >> + /* For a reference to a flexible array member, an interior zero
> >> length
> >> + array, or an array with variable length of a union, use the size of
> >> + the union instead of the size of the member. */
> >> if (TREE_CODE (argtype) == UNION_TYPE)
> >> memsize = TYPE_SIZE_UNIT (argtype);
> >> }
> >>
> >> - /* MEMBER is either a bona fide flexible array member, or a zero-length
> >> - array member, or an array of length one treated as such. */
> >> + /* MEMBER now is a flexible array member, an interior zero length
> >> array, or
> >> + an array with variable length. We need to decide its size from its
> >> + initializer. */
> >>
> >> /* If the reference is to a declared object and the member a true
> >> flexible array, try to determine its size from its initializer. */
> >> @@ -14351,6 +14347,59 @@ default_is_empty_record (const_tree type)
> >> return is_empty_type (TYPE_MAIN_VARIANT (type));
> >> }
> >>
> >> +/* Determine whether TYPE is a ISO flexible array memeber type "[]". */
> >
> > ISO C99
>
> Okay, will add this.
> >
> >> +bool
> >> +flexible_array_member_p (const_tree type)
> >
> > since you pass in a type a better name would be
> > flexible_array_type_p?
> Okay, how about “flexible_array_member_type_p”? (Since “flexible array
> member” is a complete concept).
works for me
> >
> >> +{
> >> + if (TREE_CODE (type) == ARRAY_TYPE
> >> + && TYPE_SIZE (type) == NULL_TREE
> >> + && TYPE_DOMAIN (type) != NULL_TREE
> >
> > why require a specified TYPE_DOMAIN?
>
> There are multiple places in the current GCC used the following sequence:
>
> - if (TREE_CODE (type)) == ARRAY_TYPE
> - && TYPE_SIZE (type) == NULL_TREE
> - && TYPE_DOMAIN (type) != NULL_TREE
> - && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
>
> To check whether the type is a flexible_array_member type.
> (For example, the routine “add_flexible_array_elts_to_size” in c/c-decl.cc
> the routine “finish_struct” in c/c-decl.cc
> the routine “flexible_array_type_p” in tree.cc)
>
> That’s the reason I come up with this common routine to replace all these
> sequences.
>
>
> >> + && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> >
> > and why a NULL TYPE_MAX_VALUE? Isn't an unknown TYPE_SIZE enough?
>
> Does the current FE generate such IR for a []? An array type, without
> TYPE_SIZE, with a TYPE_DOMAIN, but the MAX_VALUE of the TYPE_DOMAIN is NULL?
>
> >
> > That said, I'm not sure providing this abstraction is a good idea
> > given the use I see is in frontend code.
>
> This one is also used in middle-end, for example “flexible_array_type_p” in
> tree.cc.
That was originally in c-decl.c, seems some target wanted to use it. The
issue with this is that it tests the C frontend way of declaring a flex
array (and it is used by the frontend), but there are many other possible
representations the middle-end should classify as flex array.
The Objective C frontend also has a function named this way and it seems
to be a 1:1 copy :/
The nios2 use of the function doesn't make much sense to me - externals
should not end up in _any_ section!?
So I'd rather move this function back to where it came from, ideally
to c-family/, removing the copy in objective C ...
> >
> >> + return true;
> >> +
> >> + return false;
> >> +}
> >> +
> >> +/* Determine whether TYPE is a zero-length array type "[0]". */
> >> +bool
> >> +zero_length_array_p (const_tree type)
> >> +{
> >> + if (TREE_CODE (type) == ARRAY_TYPE)
> >> + if (tree type_size = TYPE_SIZE_UNIT (type))
> >> + if ((integer_zerop (type_size))
> >> + && TYPE_DOMAIN (type) != NULL_TREE
> >> + && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> >
> > that again seems very C(?) frontend specific, please drop it.
> Currently, the middle-end utility routine “component_ref_size” need to check
> zero_length_array, one_element_array, etc,
> So, this is not only a FE specific routine.
Sigh, it's nother strange function that was introduced just for
diagnostics (so it's not "correct"), it shouldn't have ended up in
tree.cc IMHO.
> And I think that for making the -fstrict-flex-array work clear, we might want
> to emphasize and distinguish the concepts of
>
> [] flexible_array_member_type_p
> [0] zero_length_array_type_p
> [1] one_element_array_type_p
>
> Across GCC.
Why? The only important thing to the middle-end is whether the
size of the array is known (aka array_at_struct_end_p). This
routine classifies it with
/* The array now is at struct end. Treat flexible arrays as
always subject to extend, even into just padding constrained by
an underlying decl. */
if (! TYPE_SIZE (atype)
|| ! TYPE_DOMAIN (atype)
|| ! TYPE_MAX_VALUE (TYPE_DOMAIN (atype)))
return true;
any flexible_array_member_type_p that covers a different subset of
flex-array types would be hugely confusing.
>
> >
> >> + return true;
> >> + return false;
> >> +}
> >> +
> >> +/* Determine whether TYPE is a one-element array type "[1]".
> >> + Set IS_CONSTANT_LENGTH to true if the length is constant,
> >> + otherwise, IS_CONSTANT_LENGTH is set to false. */
> >> +bool
> >> +one_element_array_p (const_tree type, bool *is_constant_length /* = NULL
> >> */)
> >> +{
> >> + if (is_constant_length)
> >> + *is_constant_length = false;
> >> +
> >> + if (TREE_CODE (type) == ARRAY_TYPE)
> >> + if (tree dom = TYPE_DOMAIN (type))
> >> + if (tree min = TYPE_MIN_VALUE (dom))
> >> + if (tree max = TYPE_MAX_VALUE (dom))
> >> + if (TREE_CODE (min) == INTEGER_CST
> >> + && TREE_CODE (max) == INTEGER_CST)
> >> + {
> >> + offset_int minidx = wi::to_offset (min);
> >> + offset_int maxidx = wi::to_offset (max);
> >> + offset_int neltsm1 = maxidx - minidx;
> >> + if (is_constant_length)
> >> + *is_constant_length = true;
> >> + if (neltsm1 == 0)
> >> + return true;
> >> + }
> >
> > I'd say likewise. Maybe move them to c-family/c-common.{cc,h} instead
> > in a more specialized way for the single use you have?
>
> It’s not single use, it’s also used in “component_ref_size” routine.
Don't copy from a routine that's not designed to be "correct". In
fact the middle-end already has array_type_nelts, so one_element_array_p
can be written as integer_zerop (array_type_nelts (type)). It also
has the comment
/* TYPE_MAX_VALUE may not be set if the array has unknown length. */
if (!max)
{
/* zero sized arrays are represented from C FE as complete types
with
NULL TYPE_MAX_VALUE and zero TYPE_SIZE, while C++ FE represents
them as min 0, max -1. */
if (COMPLETE_TYPE_P (type)
&& integer_zerop (TYPE_SIZE (type))
&& integer_zerop (min))
return build_int_cst (TREE_TYPE (min), -1);
Richard.
> Thanks a lot for your comments.
>
> Qing
> >
> >> + return false;
> >> +}
> >> +
> >> /* Determine whether TYPE is a structure with a flexible array member,
> >> or a union containing such a structure (possibly recursively). */
> >>
> >> @@ -14367,10 +14416,7 @@ flexible_array_type_p (const_tree type)
> >> last = x;
> >> if (last == NULL_TREE)
> >> return false;
> >> - if (TREE_CODE (TREE_TYPE (last)) == ARRAY_TYPE
> >> - && TYPE_SIZE (TREE_TYPE (last)) == NULL_TREE
> >> - && TYPE_DOMAIN (TREE_TYPE (last)) != NULL_TREE
> >> - && TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (last))) == NULL_TREE)
> >> + if (flexible_array_member_p (TREE_TYPE (last)))
> >> return true;
> >> return false;
> >> case UNION_TYPE:
> >> diff --git a/gcc/tree.h b/gcc/tree.h
> >> index e6564aaccb7..3107de5b499 100644
> >> --- a/gcc/tree.h
> >> +++ b/gcc/tree.h
> >> @@ -2993,6 +2993,11 @@ extern void decl_value_expr_insert (tree, tree);
> >> #define DECL_PADDING_P(NODE) \
> >> (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_3)
> >>
> >> +/* Used in a FIELD_DECL to indicate whether this field is not a flexible
> >> + array member. */
> >> +#define DECL_NOT_FLEXARRAY(NODE) \
> >> + (FIELD_DECL_CHECK (NODE)->decl_common.decl_not_flexarray)
> >> +
> >> /* A numeric unique identifier for a LABEL_DECL. The UID allocation is
> >> dense, unique within any one function, and may be used to index arrays.
> >> If the value is -1, then no UID has been assigned. */
> >> @@ -5531,10 +5536,10 @@ extern tree component_ref_field_offset (tree);
> >> returns null. */
> >> enum struct special_array_member
> >> {
> >> - none, /* Not a special array member. */
> >> - int_0, /* Interior array member with size zero. */
> >> - trail_0, /* Trailing array member with size zero. */
> >> - trail_1 /* Trailing array member with one element. */
> >> + none, /* Not a special array member. */
> >> + int_0, /* Interior array member with size zero. */
> >> + trail_0, /* Trailing array member with size zero. */
> >> + trail_1 /* Trailing array member with one element. */
> >> };
> >>
> >> /* Return the size of the member referenced by the COMPONENT_REF, using
> >> @@ -6489,6 +6494,9 @@ extern void gt_pch_nx (tree &, gt_pointer_operator,
> >> void *);
> >> extern bool nonnull_arg_p (const_tree);
> >> extern bool is_empty_type (const_tree);
> >> extern bool default_is_empty_record (const_tree);
> >> +extern bool zero_length_array_p (const_tree);
> >> +extern bool one_element_array_p (const_tree, bool * = NULL);
> >> +extern bool flexible_array_member_p (const_tree);
> >> extern bool flexible_array_type_p (const_tree);
> >> extern HOST_WIDE_INT arg_int_size_in_bytes (const_tree);
> >> extern tree arg_size_in_bytes (const_tree);
> >>
> >
> > --
> > Richard Biener <rguent...@suse.de>
> > SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> > Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> > HRB 36809 (AG Nuernberg)
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
